We report on the precessional dynamics in spin transfer oscillators having Co60Fe20B20 free layers as a function of annealing time at 225 °C. Repeated annealing reduces the critical current Ic by roughly a factor of 3 and increases the tunability of the oscillation frequency with current df/dI. The decrease in Ic correlates with an increasing giant magnetoresistance (GMR) during the first 3 h of annealing. For longer times, df/dI continues to increase, although the GMR does not. The variations in the macroscopic Co60Fe20B20 magnetization parameters and contact dimensions with annealing are not sufficient to account for the later changes.